ngoncom: - Titans can't attack far (ranged attack), he often attack far with thunder but sometime he can't
If an enemy unit is next to a ranged unit, the ranged unit cannot use their ranged attack. A common tactic is to put a melee unit next to an opponent's ranged stack, even if you don't attack the ranged stack, to stop them from shooting (and also cut their damage in half; unless a ranged stack has "No melee penalty" then they deal half damage with melee attacks).
Also, as rmontiago said, keep track of your ammo. Most fights don't last long enough for this to be a problem, but a few units (especially Medusa) have a very limited number of shots. An Ammo Cart allows a unit to shoot without decrementing their ammo count.
ngoncom: - When auto combat, Archangel can cast resurrection but when I play, I can't let him cast
When the Archangels are active, mouse over the target stack you want to resurrect.
-The target stack must have lost at least one creature. You can't use the spell just to heal an injured creature.
-The target stack can't be blocked by having something standing in the same hex as their corpse (not a problem if you want to resurrect a stack that still has a least one creature still alive).
-Not all units can be resurrected. Undead, golems, elementals, and machines can't be affected by resurrection.
-The target stack can't be immune to Resurrect. Black Dragons and Gold Dragons are both immune to level 4 spells, so neither one can be resurrected even though they are living creatures. If you've cast a strong enough Anti-Magic Shell on the target, the Archangels can't resurrect it while the spell is active.
-A given Archangel stack can only cast Resurrect once per battle. You can split up your archangels to get more resurrects, but stack size affects the Power used to cast Resurrect (a stack of 50 archangels casts a stronger Resurrect than a stack of 5 archangels).
-Cursed Lands (a terrain type) and I think the Recanter's Cloak (an artifact) can each block the casting of Resurrect.
Montiago mentioned stacked corpses; I don't recall whether it matters.
ngoncom: - Enemy's hero hidden himself, I can't see him on map; and suddenly he appears and attack my castle
He could have walked out of the fog. He could have flown or water walked. He could have used a map teleporter. He could have used the Dimension Door spell.
ngoncom: That makes sense to me, thank you so much! Happy New Year!
More of a formality: if you have the answer to your question, then please mark the relevant post as the answer. That way others can see the question has been answered.
Happy New Year!